<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <p>点击按钮,在等待 3 秒后弹出 "Hello"。</p>
    <button onclick="myFunction()">点我</button>
    <script>
         function myFunction(){
            setTimeout(function(){
                alert('hello')
            },3000);
         };
    </script>
    
</body>
</html>